The instant invention relates to water treatment processes, and more particularly, to a novel composition for the bactericidal treatment of water.
It is widely known that chlorine can be effectively used to kill bacteria contained in water. Chlorine is commonly used for treating drinking water, and also for treating water used in swimming pool systems, and it is even used to treat waste water during sewage treatment processes. However, while the addition of chlorine to water has been found to be an effective method of killing bacteria contained in the water, it has a number of disadvantages. First, chlorine, which is a relatively volatile gas in its natural state, is rapidly dissipated from water which is left to stand open to the atmosphere, particularly when the water has a temperature of greater than approximately 70 degrees fahrenheit. Therefore, it is generally necessary to make frequent additions of chlorine to water under these conditions in order to maintain the bacteria levels in the water within safe ranges, and obviously this has disadvantages from both practical and economic standpoints. Further, while the necessity for frequently replenishing chlorine levels in water represents a major drawback to the use of chlorine for the germicidal treatment of water, there are several other disadvantages which specifically apply to the use of chlorine for the treatment of water used in open pools, such as swimming pools, hot tubs, soaking tubs and the like. In particular, chlorine produces a distinct odor as it is dissipated from an open pool of water, and this has been found to be objectionable to many swimmers and bathers. In addition, water containing high concentrations of chlorine can be harmful to the eyes of swimmers and bathers after prolonged periods of exposure and, to a lesser extent, water containing high levels of chlorine can be harmful to the skin and hair. Further, because the dissipation of chlorine from a pool of water is substantially accelerated when the water is heated to an elevated temperature level, chlorine is often dissipated so rapidly from hot tubs and soaking tubs that it is difficult or impossible to reliably maintain chlorine levels in these tubs within the desired ranges. This, combined with the fact that the growth of bacteria is substantially accelerated by elevated temperature levels, makes the use of chlorine frequently unsatisfactory for hot tub and soaking tub applications.
The use of heavy metals, in particular, heavy metals of the type commonly referred to as oligodynamic metals for the bactericidal treatment of water is also widely known. More specifically, it is known that ions of oligodynamic metals, especially silver ions, have a bactericidal effect when they are present in water, even at relatively low concentration levels, such as below 50 parts per billion. As a result, it is generally accepted that oligodynamic metal ions can be effectively utilized to maintain bacteria levels in water within tolerable ranges which permit the safe use of the water for swimming or drinking purposes. On the other hand, however, it is also recognized that excessive concentration levels of oligodynamic metal ions in water can be toxic or harmful to humans. Generally, it has also been found that silver ions are the most effective oligodynamic metal ions for the bactericidal treatment of water, and it has been found that silver ion concentration levels of up to 50 parts per billion can be safely tolerated by humans without adverse effects. Further, it has been found that silver ion concentration levels in the range of between 10 and 50 parts per billion can be generally effective for maintaining the bacteria concentrations in water within tolerable ranges. In any event, in order to utilize silver ions to effectively kill bacteria in a water treatment system, some mechanism must be provided for releasing silver ions at rates which can be effectively controlled so that the overall silver ion concentrations in the water can be maintained within a safe range of between approximately 10 and 50 parts per billion. Further, for practical reasons, it is important for a system of this type to be able to maintain the silver ion concentration level in the quantity of water within a desired range over a prolonged period of time without requiring significant amounts of attention.
While a variety of systems have been heretofore available which have utilized oligodynamic metals for the bactericidal treatment of water, generally, the heretofore known technology has failed to provide an effective means for releasing silver ions into a contained system, such as a swimming pool, at a controlled rate over a prolonged period of time. In this regard, most of the known systems have comprised apparatus which is operative for releasing silver ions at relatively high rates, but not at slow rates which can be effectively controlled over prolonged periods of time. Hence, while the known systems can be utilized for adding large quantities of silver ions to previously untreated water to kill the bacteria contained therein, they generally release silver ions at rates which are far too high for use in maintaining silver ion levels in contained or closed systems, such as swimming pool systems, after the desired ion levels have initially been reached. In many cases, this is because systems have utilized silver salts, which are highly soluble in water, as the sources of silver ions and these salts have typically released silver ions at rates which are far too high to be effectively controlled over prolonged periods in contained systems such as swimming pool, soaking tub, and hot tub systems. While water treatment systems have also been available which have utilized elemental silver which is dissolved very, very slowly in water to produce silver ions, these systems have generally not released ions at rates which are sufficient to permit their use for maintaining ion concentrations in contained systems, and generally the known systems of this type have also been ineffective for prolonged use.
The instant invention provides an effective composition and method for releasing silver ions into water at controlled practical rates over prolonged periods of time so that the composition and method can be effectively utilized in essentially closed systems. In this regard, the composition of the instant invention from which silver ions are released comprises a silver yielding material comprising a carrier having a particle size of between 4 and 20 mesh and a layer of elemental silver on the surfaces of the carrier, and a filler material also having a particle size of between 4 and 20 mesh which is intermixed with the silver yielding material. The carrier has a relatively high porocity which provides a surface area of greater than 150 square inches per gram and it has a Mohs scale hardness which is greater than that of silver, i.e. greater than 2.5. The carrier is also substantially insoluble in water having a pH of between 5 and 9. The carrier preferably consists of alumina which has a hardness of greater than 9 on the Mohs scale, a porocity which provides a surface area of approximately 210 square inches per gram, and a particle size of between 8 and 14 mesh, and preferably the alumina is activated to provide a greater bond strength between the carrier and the silver on the surfaces thereof. The silver is preferably distributed over both the interior and exterior surfaces of the porous carrier and it preferably comprises between 1% and 10% by weight of the total silver yielding material. The filler material which is intermixed with the silver yielding material has a hardness which is less than that of silver, i.e. less than 2.5 on the Mohs scale, and it is intermixed with the silver yielding material so that the ratio of filler material to silver yielding material is between approximately 1:1 and 5:1. Preferably, the filler material has a particle size which is substantially the same as that of the silver yielding material, and it is intermixed therewith in a ratio of approximately 2:1 and, preferably, the filler material consists essentially of activated charcoal.
For practicing the method of the instant invention, to treat a pool of water, a stream of water is drawn from the pool and passed through the composition of the instant invention and then returned to the pool and the flow rate of the stream is controlled to maintain the concentration of silver ions in the pool at a level of between 10 and 50 parts per billion. It has been found that because of the make-up of the composition of the instant invention, it can be effectively utilized for providing controlled additions of silver ions to a body of water at rates which are practical for most pool systems, and it has also been found that the composition can be utilized over a prolonged period of time to maintain the silver ion concentration level in a pool within a desired range. Further, because of the make-up of the composition of the instant invention and the effectiveness with which it can provide controlled releases of silver ions into a stream of water, the method and composition of the instant invention can be readily adapted for use in most conventional swimming pool and soaking tub systems. More specifically, when a quantity of the composition of the instant invention is contained in a relatively small canister, the canister can be readily utilized in a conventional swimming pool or soaking tub system simply by connecting the canister to the otherwise conventional filtration system of the swimming pool or soaking tub system. This is because the composition of the instant invention is effective for releasing silver ions to maintain the desired silver ion levels in swimming pool or soaking tub systems when relatively small quantities of the composition are exposed to water flow rates which are normally within the ranges of flow rates provided by conventional filtration system equipment. Hence, the composition and method of the instant invention can be utilized in most conventional swimming pool and soaking tub systems simply by connecting a canister containing a quantity of the composition to existing or conventional equipment of the system. This provides substantial practical advantages for the method and composition of the instant invention.
The closest prior art to the instant invention of which the applicant is aware is disclosed in the U.S. patents to Conconi (U.S. Pat. No. 2,283,883), Renn (U.S. Pat. No. 3,268,444), Nishino et al (U.S. Pat. No. 3,872,013), and Beauman et al (U.S. Pat. No. 4,396,512); the United Kingdom patents to Krause (Nos. 279,085 and 353,686), the German patent to Mitsumori et al (No. 2,505,597), and the Japanese KoKai publication No. 74 97,730 by Tsukada et al. However, none of these references suggest the combination of a relatively hard silver yielding material with a relatively soft filler material to provide a composition having the silver release properties of the composition of the instant invention. Hence, these references are felt to be of nothing more than general interest.
Accordingly, it is a primary object of the instant invention to provide an effective composition which can be utilized to release silver ions into water at a slow controlled rate in a closed system, such as a swimming pool, soaking tub, or hot tub system.
Another object of the instant invention is to provide an effective method of releasing silver ions into a pool of water which permits the overall silver ion concentration in the pool to be effectively controlled.
Another object of the instant invention is to provide an effective method of releasing silver ions into a swimming pool which permits the overall silver ion concentration in the swimming pool to be maintained at between 10 and 50 parts per billion.
An even further object of the instant invention is to provide a method of releasing silver ions into water at a slow controlled rate utilizing a silver yielding material, wherein the silver yielding material is operative over a prolonged period of time.